The human serological response to several envelope-associated proteins and adenylate cyclase toxin of B. pertussis was examined using immunoblot techniques. Antigens recognized by sera from individuals with culture-confirmed pertussis as well as by sera from infants immunized with three doses of conventional whole-cell pertussis vaccine included a 63,000 Da protein that was shown to be antigenically related to a mycobacterial heat-shock protein and structurally related to the chaperonin family of proteins involved in protein folding and assembly. B. pertussis lipooligosaccharide was also recognized by antibodies in certain of these sera. A 29,000 Da species reacted with sera from convalescent individuals whereas a 91,000 Da species reacted with sera from vaccinated individuals. Antibodies to adenylate cyclase toxin were common in sera from individuals diagnosed with pertussis, however these antibodies were rarely found in children who had received three doses of DTP vaccine. These data suggest that some of these antigens may play a role in immunity to pertussis and that further investigation is warranted.